The present invention relates to a packaged micro-mechanical devices with an optical interface, and in particular, to an optical interface reference plane adjacent to the optical micro-mechanical device that is useful for aligning optical fibers.
Fabricating complex micro-electro-mechanical systems (MEMS) and micro-optical-electro-mechanical systems (MOEMS) devices represents a significant advance in micro-mechanical device technology. Presently, micrometer-sized analogs of many macro-scale devices have been made, such as for example hinges, shutters, lenses, mirrors, switches, polarizing devices, and actuators. These devices can be fabricated, for example, using Multi-user MEMS Processing (MUMPs) available from Cronos Integrated Microsystems located at Research Triangle Park, North Carolina.
One method of forming a MEMS or MOEMS device involves patterning the device in appropriate locations on a substrate. As patterned, the device lies flat on top of the substrate. For example, the hinge plates of a hinge structure or a reflector device are both formed generally coplanar with the surface of the substrate using the MUMPs process. Applications of MEMS and MOEMS devices include, for example, data storage devices, laser scanners, printer heads, magnetic heads, micro-spectrometers, accelerometers, scanning-probe microscopes, near-field optical microscopes, optical scanners, optical modulators, micro-lenses, optical switches, and micro-robotics.
Packaging MEMS devices presents unique problems due to the physically active nature of the microstructures. To maintain a stable environment and to keep out dust particles, corrosive and/or potentially fouling vapors, etc., the micro-machined structures must be enclosed within a sealed package. A sealed package also minimizes the risk of physical damage during handling or operation. Traditional integrated circuit encapsulation methods such as epoxy resin potting and thermoplastic injection molding, while useful with integrated circuits, which have no moving parts, are incapable of use directly with micro-machined structures. The encapsulant must not contact the active portions of the micro-machined structure. Moreover, common encapsulation techniques such as injection molding, often requiring pressures of 1000 psi, would easily crush the microstructure.
One application for micro-machined structures is in connection with processing optical signals, such as optical switches, wavelength specific equalizers, polarization mode dispersion compensators, and the like. These applications, however, require coupling optical fibers with the packaged micro-machined structures. Various techniques are known for packaging MEMS devices, such as disclosed in U.S. Pat. No. 6,146,917 (Zhang et al.) EP0852337; and EP1057779. None of these packaging techniques, however, teach coupling optical fibers to the MEMS device.
The present invention is directed to a packaged optical micro-mechanical device with an optical interface reference plane adjacent to the micro-mechanical devices. One or more optical micro-mechanical devices are located on a first surface of a die. The first surface includes a die reference surface. A package frame comprising an aperture and a package frame reference surface proximate the aperture is adapted to receive the die reference surface such that the optical micro-mechanical devices are located in the aperture. One or more optical interconnect alignment mechanisms, such as V-grooves, terminate adjacent to the aperture and are positioned relative to an optical interface reference plane. Distal ends of one or more optical interconnects, such as optical fibers are located in optical interconnect alignment mechanisms and are optically coupled with one or more of the optical micro-mechanical devices.
The optical interface reference plane can be the die reference surface, the package frame reference surface or a plane parallel to the die reference surface located between the die reference surface and the package frame reference surface. Locating the optical interface reference plane near to the plane containing the optical interconnects improves alignment and minimizes tolerance build-up.
The optical interconnect alignment mechanisms can be located in the package frame reference surface, in the die reference surface or in both the package frame reference surface and the die reference surface. The optical interconnects can have tangential relationship with the optical interface reference plane. In another embodiment, a first portion of the optical interconnect is positioned on one side of the optical interface reference plane and a second portion of the optical interconnect is positioned on another side of the optical interface reference plane.
In one embodiment, the optical interconnect contacts the die. In another embodiment, the optical interconnect terminate adjacent to the die without contacting the die. In another embodiment, lenses located in the V-groove are optically coupled to the distal end of the optical fiber. The lenses optically couple the optical fiber with one or more optical micro-mechanical devices. The lens can contact the die or can terminate adjacent to the die without contacting the die.
One or more contact pads can optionally be interposed between the die reference surface and the package frame reference surface. The contact pads can be located on the die reference surface and/or the package frame reference surface. In one embodiment, the contact pads electrically couple one or more optical micro-mechanical devices with external electrical contacts, such as contact pads located on the package frame reference surface. In another embodiment, the contact pads electrically couple one or more optical micro-mechanical devices with a flexible circuit member. The contact pads can also be used to mechanical attach the die to the package frame.
The aperture can be a rectangular shape or a complex shape. In one embodiment, the aperture comprises a cross-shape configured so that the distal ends of the optical fibers terminate in arms of the cross-shaped aperture without contacting the die.
A tooling fixture can be located on a rear surface of the die. The tooling fixture can be a tooling post and/or a heat sink. An encapsulating material is typically used to seal the die to the package frame. A cover seals the die to the package frame.
A flexible circuit can be electrically coupled to the die. In one embodiment, the flexible circuit extends across a rear surface of the die and one or more vias extend through the die and electrically coupling the optical micro-mechanical devices to the flexible circuit. In another embodiment, a shoulder region is formed adjacent to the optical micro-mechanical devices. Electrical traces extend from the optical micro-mechanical devices to the shoulder region. A flexible circuit is located between the shoulder region and the optical interface reference plane. The flexible circuit is electrically coupled to the traces.
In one embodiment, the package frame comprises one or more alignment posts position to engage with the die reference surface. A cavity is preferably formed adjacent to the alignment posts on a side opposite the aperture. A flexible circuit extending through the cavity electrically couples with contact pads on the die reference surface. An adhesive located in the cavity can be used to retain the die to the alignment posts.
The present invention is also directed to an optical communication system including at least one packaged optical micro-mechanical device in accordance with the present invention.